The cup of this invention is particularly adapted to use with the heating units of the types shown and described in U.S. Pat. Nos. 3,876,861 and 4,160,152, but its utility is not confined to that use. It is desirable for both economic and esthetic reasons to be able to use a moderate temperature, inexpensive plastic such as polypropylene to make cups. However, when a heat conductive stainless steel closure is to be used to cover and seal an opening in the bottom of the cup, so as to provide better heat transfer through the bottom, the use of plastic such as polypropylene poses a problem. The plastic has a high coefficient of expansion as compared with the metal. Furthermore, it tends to take a permanent set, particularly when it is confined near the outer limit of its expansion, and then to contract upon cooling so that a tight circumferential fit between the plastic and the metal becomes progressively looser as the plastic first sets at its outer limit and then contracts inwardly. With the construction of this invention, a moderate temperature, relatively inexpensive plastic can be used to produce a cup with a stainless steel bottom closure sealed and accomodated for differences in expansion and contraction by a thin, e.g. 20 mil, silicone gasket.
One of the objects of this invention is to provide a cup with a plastic body and a metal base closure which will remain liquid-tight after repeated heating and cooling.
Another object is to provide method and apparatus for producing such a cup simply, economically and effectively.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.